Study I: Subjects (n equals 50) were challenged to respond rapidly and accurately on three tasks while the experimenter monitored physiological responses. Type A subjects showed significantly greater cardiovascular changes indicative of sympathetic ANS arousal than Type B subjects. Study II: Cardiovascular reactivity of male Type A (n equals 44) and B (n equals 36) subjects to a cold pressor and reaction time test was measured under high and low instructional conditions. Under high but not low challenge instructions, Type A subjects showed greater levels of cardiovascular arousal than their Type B counterparts while working on both tasks. Additional results suggest that high hostile A's may be prone to respond to even low levels of social or physical challenge with enhanced arousal. Study III: The Structured Interview used to assess the Type A pattern was compared to questionnaire methods of assessment. Results showed only weak agreement between methods in designating subjects as Type A and B. Study IV: Coronary patients (n equals 31) and patient controls (n equals 33) were subjected to an interview and a history quiz. Type A relative to Type B subjects evidenced significantly greater increases in both systolic and diastolic blood pressure. In addition, the quiz induced significant elevations in the blood pressure of coronary patients, but not patient controls, over that displayed during the interview, despite the presence of beta adrenergic blocking medication.